Oscilloscope having external trigger display mode

ABSTRACT

An oscilloscope has an additional vertical display mode to enable the display of an external triggering signal while it is activating the sweep-generating circuit. Triggering source, level, slope, and timing can be verified or examined without reconnection of signal cables or disturbing front-panel controls. When switching between vertical display modes, the displayed external triggering signal is in precise time relationship with signals displayed through normal vertical channels.

Unite States Patent 11 1 1111 3,795,834

Andrews et al. Mar. 5, 1974 [54] OSCILLOSCOPE HAVING EXTERNAL 3,559,082l/l97l Horn 328/181 TRIGGER DISPLAY MODE [75] Inventors: Roland EugeneAndrews, Portland; Primary Exami' 'er Maynard Wilbur Robert Edward WhiteAloha, both Assistant Exammer.l. M. Potenz'a of Greg Attorney, Agent, orFirm-Adrian J. La Rue [73] Assignee: Tektronix, Inc., Beaverton, Oreg.

. [57] ABSTRACT [22] Filed: July 5, 1972 An oscilloscope has anadditional vertical display [21] PP N04 2691006 mode to enable thedisplay of an external triggering signal while it is activating thesweep-generating cir- [52] U.S. Cl. 315/26 cuit- Triggering Source levelslope and timing can be 51 Int. Cl. H01j 29/70 verified examined Withoutrewmeclkm Signal 58 Field 01 Search 328/181; 315/26, 27 R; cables ofdisturbing from-Panel Commiswhen 178/75 5 switching between verticaldisplay modes, the displayed external triggering signal is in precisetime rela- [56] References Cited tionship withsignals displayed throughnormal vertical UNITED STATES PATENTS Channels 3,599,034 8/1971 Fischer315/26 9 Claims, 4 Drawing Figures TO VERTICAL AMPLIFER AND CRT

DEFLECT- ION PLATES PATENTEDu/m 5 m4 SHEET 1 0F 2 ERTICAL AMP 24 S DELAYLINE 422 HORIZ AMP 22 I L VERTICAL IMODE I'- sE ECT VERTICAL CHANNELSELECTOR I SWEEP GEN SWEEP Flg-l RING EXT TRIG PREAMP GATE VIEW AMPTRIGGER SOURCE AND COUPLING LINE TRIG SIG VERTICAL AMPLIFER AND CRTDEFLECT- ION PLATES DELAY I 34 w ssl l TRIGGERING LEVEL 2% TO SWEEPGATING CIRCUIT SOURCE TRIGGERING LEVEL REFERENCE WAVEFOFIM OF SIGNAL IAT INPUT TERMINALS L I0 AND 30 WAVEFORM 0F SIGNAL AT INPUT TO DELAY LINE24 INHERENT DELAY 0F VERTICAL PREAMPLIFIER" TRIGGER PULSE DELAY m SWEEPGENERATOR SWEEP-(EATING SIGNAL SWEEP-D vERTlcAL LOCATION OF wAvE SIGNALAT FORM DEPENDS ON vERTlcAL HORIZONTAL POSITION CONTROL DEFLECTIONPLATES DELAYED WAVEFORM OF SIGNAL AT VERTICAL (A) NORMAL VERTICALDISPLAY DEFLECTION PLATES DELAY INTRODUCED BY DELAY LINE 24 VERTICALLOCATION OF WAVEFORM DEPENDS ON TRIGGERING LEVEL CONTROL (B) EXTERALTRIGGERING SIGNAL DISPLAY Fig-4 OSCILLOSCOPE HAVING EXTERNAL TRIGGERDISPLAY MODE BACKGROUND OF THE INVENTION Conventional triggerableoscilloscopes generally have at least three sweep triggering modes:internal, line, and external. In the internal triggering mode, a signalfor display is applied to the vertical input terminal. A sample of thedisplay signal is derived from the vertical preamplifier and routedinternally to the triggergenerating circuit. A sweep is initiated whenthe display signal passes through a pre-selected reference level. Sincethe sweep generator has an inherent time delay from the time a triggeris produced until the time the display actually starts on thecathode-ray tube screen, the display signal is deliberately delayed toallow leading-edge portion of a rapid changing waveform to be seen.

In the line-triggering mode, a repetitive sweep is synchronized with thepower-line frequency, whether a vertical display signal is available ornot. A sample of the power-line A. C. voltage is derived from the powerinput circuit and routed internally to the triggergenerating circuit.There is generally no need to view the triggering signal in this modebecause of its known frequency, shape, and stability. For this mode tobe useful, the vertical display signal must be time-related to the linefrequency.

In the external triggering mode, the triggering signal is applied froman external source, such as a signal generator or a reference point in acircuit under test, directly to the trigger-generating circuit via anexternal trigger input terminal. A sweep is initiated when thetriggering signal passes through a pre-selected reference level. Thismode is useful when the vertical display signal must be observed in itsrelationship to another event.

Sometimes it is necessary to verify the external triggering source, orcheck the triggering level or slope, etc., by examining the triggeringwaveform. Previously, this required that the vertical display signal bedisconnected from the vertical input terminal, then the externaltriggering signal moved from the external triggering input terminal tothe vertical input terminal. Then the triggering source and levelcontrols, the vertical deflection sensitivity, vertical position, andattenuator controls required readjusting with little assurance thattriggering could be achieved at the proper point on the waveform. Afterthe check was completed, all the signal cables and controls had to bereturned to the initial conditions. Consequently, the operation wascomplicated, time consuming, inconvenient, and subject to error.

SUMMARY OF THE INVENTION According to the present invention, anadditional vertical display mode has been added to a conventionaloscilloscope to permit observation of an external triggering signal bysimply actuating a switch. Additionally, the exact point on thetriggering signal waveform at which the sweep is initiated can beprecisely located. A trigger-view preamplifier circuit comprising abalanced differential amplifier receives both the external triggeringsignal and the triggering level reference voltage from a portion of thetrigger input circuit. The .pushpull output of the trigger-viewpreamplifier circuit is switched into the vertical-channel delay line,processed by the vertical output amplifier, and applied to the verticaldeflection plates of the cathode-ray tube (CRT). Overall delay of thetrigger-view preamplifier is matched to the overall delay of the normalvertical preamplifier stage, allowing the leading edge of a rapidlychanging external triggering waveform to be observed as is the casepreviously described for conventional internally-triggered displays.Also, since the triggerview preamplifier is a balanced differentialamplifier, vertical screen center corresponds to the level set by thetriggering level control. Thus the oscilloscope operator can achievestable triggering on a desired point on the external triggering signalbecause he can see the triggering level in relation to the triggeringwaveform.

It is therefore one object of the present invention to provide anoscilloscope display of an external triggering signal waveform while itis triggering the time-base sweep without changing signal connections ordisturbing any controls of the oscilloscope.

It is another object of the present invention to provide a simple meansfor precisely locating the point on the triggering waveform at which atime-base sweep is initiated.

It is still yet another object of the present invention to provide asimple means for identifying or verifying an external triggering source.

It is a further object of the present invention to provide anoscilloscope display of an external triggering signal in the precisetime-position relationship to a signal applied to the normal verticalamplifier channel.

Other objects and attainments of the present invention will becomeapparent to those skilled in the art upon a reading of the followingdetailed description when taken in conjunction with the drawings inwhich there is shown and described a block diagram and an illustrativeembodiment of the invention; it is to be understood, however, that thisembodiment is not intended to be exhaustive nor limiting of theinvention but is given for purposes of illustration in order that othersskilled in the art may fully understand the invention and principlesthereof and the manner of applying it in practical use so that theymodify it in various forms, each as may be best suited to the conditionsof the particular use.

DRAWINGS FIG. 1 shows a simplified block diagram of an oscilloscope inwhich the relationship of the present invention to the conventionalcircuits is shown,

FIG. 2 shows a schematic of the preferred embodiment according to thepresent invention,

FIG. 3 shows a waveform ladder diagram of important waveforms accordingto the present invention, and

FIG. 4 shows identical waveforms displayed on a cathode-ray tube screenin (A) normal vertical mode and (B) external trigger display mode.

DETAILED DESCRIPTION Referring to FIG. 1, the block diagram of a largelyconventional oscilloscope having two vertical amplifier channels isshown. A signal to be displayed on the cathode-ray tube screen isapplied to either channel 1 or channel 2 input terminal 10 or 11. Inputcircuit 14 or 15 provides correct attenuation and coupling, then thesignal receives its first amplification and is split into a push-pull,or differential output by preamplifier 16 or 17. Preamplifiers 16 and R7generally include gain switching to provide a plurality of verticaldeflection factors, and they also generally provide a sample of thedisplay signal to the time-base triggering circuit. The channel to beviewed is selected by vertical channel selector 18, then the signal isrouted via the closed contacts of vertical mode selector 22 (to bediscussed later) to the delay line 24. Delay line 24 is designed todeliberately delay the display vertical information to allow theinternal triggering signal to activate the sweep generator circuits,thus ensuring no loss of the display information. The signal receives afinal amplification ,by vertical amplifier 26 and is then applied tovertical deflection plates 28 of the cathode-ray tube 29. The triggeringsource and coupling switches 32 select a suitable triggering signal frominternal, line, or external sources and provide the desired coupling ofthe triggering signal to the trigger preamplifier 34. Generally, triggerpreamplifier 34 is a comparison amplifier, comparing the triggeringsignal to a reference voltage established by potentiometer 36, andproducing a trigger when the triggering signal voltage passes throughthe reference level. Upon receipt of a trigger, sweep gate 38 produces avoltage which turns on sweep generator 40, producing a sawtooth voltagewhich is split into a differential signal and amplified by horizontalamplifier 42 to levels suitable to drive horizontal deflection plates 44in a linear fashion. In most conventional oscilloscopes, sweep gate 38is a bistable multivibrator, and sweep generator 40 is a Millerintegrator.

The novelty of the present invention is the addition ofa verticaldisplay mode to permit viewing an external triggering signal while sucha signal is activating the sweep circuits. A triggering signal appliedfrom an external source to input terminal 30 is selected by thetriggering source and coupling switches 32, and applied to the input ofthe trigger preamplifier in the conventional fashion. However, thetriggering signal, together with the reference level from potentiometer36, is also routed to external trigger-view preamplifier 20. The outputfrom preamplifier is passed through coaxial cables 21 to the verticalmode selector 22. Vertical rnode selector 22 selects the display signalfrom either the normal vertical preamplifier channel or the triggerviewpreamplifier.

FIG. 2 shows a schematic of the preferred embodiment according to thepresent invention. As described previously, a display signal applied toinput terminal 10 is preamplified and split into a push-pull signal byvertical preamplifier 16. The push-pull output is applied via switchcontacts 22A and 228 to delay line 24. For clarity in comparing timerelationship and displays, assume that an identical signal is applied tothe external triggering input terminal in normal practice, these signalswould usually be different or at least not coincident. The waveformsshown in FIG. 3, therefore, apply to both modes of operation, while FIG.4 shows the displays of these waveforms. For this discussion, thetriggering source switch 50 is in the EXT position as shown. Thetriggering signal passes through switch contacts 50A and through theclosed contacts of the coupling switch 511 to the input ofa triggerpreamplifier circuit 34. Trigger preamplifier 34 includes transistors 54and 56, which are emitter coupled through resistor 58 to form acomparison amplifier. Resistors 52-62 and 36-60 establish biasingconditions for transistors 54 and 56 respectively. The triggering signalat the base of transistor 54 is compared to a voltage level between +Vand V set at the base of transistor 56 by potentiometer 36, establishingthe point on the triggering waveform at which it is desired to initiatea sweep signal. The triggering signal and triggering level referencevoltage are transmitted via the base-emitter paths of transistors 54 and56 respectively to the two inputs of a trigger-view preamplifier 20.While the preferred embodiment shows these signals routed through aportion of the trigger preamplifier circuit 34, an alternativeembodiment could employ separate emitter followers for this function.

Thus the external triggering signal and the triggering level referencevoltage are applied to the two input terminals ofa trigger-viewpreamplifier 20, which is a bal anced differential amplifier. Thiscircuit 20 includes a pair of emitter-coupled transistors 64 and 66,whose base input is developed across the coupling resistor 58. Theemitters of transistors 64 and 66 are coupled together through aparallel combination of resistors 68, 70, 72, and 74, across which thetriggering signal is developed. The emitters of transistors 64 and 66are returned to the negative voltage supply V through bias resistors 68and 70. Resistor 74 provides an adjustment to balance the two halves ofthe amplifier, and hence the two vertical deflection plates, when thevoltage potentials at the bases of transistors 64 and 66 are equal.Thus, it can be seen that the displayed trigger level reference isestablished at CRT screen center, for the bases of transistors 64 and 66are equal at the triggering point on the waveform.

Two sets of emitter-coupled transistor pairs 74-76 and 7880, which areNPN transistors in this embodiment, are connected to the collectors ofthe transistors 64 and 66 respectively. The bases of transistors 74 and80 are connected together to a suitable positive reference voltage +REF,and the bases of transistors 76 and 78 are connected together through abias resistor 92 to a suitable voltage source +V higher than +REF in themode shown (switch open). Therefore, for conventional oscilloscopeoperation, that is, when it is not de sired to view the externaltriggering signal, the collector currents of transistors 64 and 66 flowthrough conducting transistors 76 and 73 and are summed at thecollectors of transistors 76 and 78. Then the current is divided inhalf, and the half amount flows through each diode 82 and 84 andcollector-load resistors 86 and 88, maintaining a no-signal DC balanceat the trigger-view preamplifier 20 output.

To view the external triggering signal, the contacts of switch 90 areclosed, grounding the cathode of diode 94 and one side of relay 22. Withconduction of diode 94, the bases of transistors 76 and 78 are one diodejunction above ground and the bases of resistors 74 and 30 are at ahigher potential, +REF. Therefore, transistors 76 and 78 turn off andtransistors 74 and 80 turn on. Simultaneously, relay 22 energizes,switching the delay line input from the vertical preamplifier 16 out putto the trigger-view preamplifier 20 output. The triggering signaldeveloped across emitter resistor 72 is then amplified and a push-pulloutput is developed across the collector-load resistors 86, 87, and $8.The push-pull output is then passed through coaxial cables 211A and 228,the switch contacts 22A and 22B, and into the vertical output amplifierchannel for display on the CRT screen. As mentioned previously, coaxialcables 21A and 2llB provide the required delay match to that of verticalamplifier 16. Thus, as can be seen in FIGS. 3 and 4, if identicalsignals are applied to input terminals and 30, no horizontal shift ofthe waveform will be observed when switching the vertical mode switch 22between the normal vertical display mode and the external triggerdisplay mode. Furthermore, in the external trigger display mode, theexact triggering point on the external triggering signal waveform can belocated at the point where the waveform crosses the center horizontalline of the graticule scale. Of course, triggering slope can also bedetermined from observation of the slope of the waveform at thetriggering point.

The foregoing preferred embodiment comprises integrated circuits forhigh-frequency, low-power operation, however, it should be pointed outthat the basic circuit could be fabricated of discrete transistors ofeither NPN or PNP type, and that switching means other than a relaycould be employed without departing from the scope and spirit of thepresent invention.

It will, therefore, be appreciated that the aforementioned and otherdesirable objects have been achieved; however, it should be noted thatthe particular embodiment of the invention, which is shown and describedherein, is intended as merely illustrative and not as restrictive of theinvention.

We claim:

1. In an oscillographic instrument for providing a display of electricalsignals; said instrument including vertical deflection means forgenerating a first vertical deflection signal in accordance with theinstantaneous amplitude of a first electrical input signal fordetermining the amplitude of a waveform thereof; said instrument alsoincluding horizontal deflection means for generating a horizontaldeflection signal for providing a time-base sweep signal, said sweepsignal being generated in response to the output of a trigger comparatormeans whose inputs are a selective second electrical input signal and aselective reference voltage, wherein said second electrical signal iscompared to said selective reference voltage; the improvementcomprising:

means for receiving said second electrical and said selective referencevoltage from said trigger comparator means and generating a secondvertical deflection signal in response thereto, said second verticaldeflection signal being generated in accordance with the amplitude ofsaid second electrical signal and in comparison to said referencevoltage for determining the sweep-initiating point on the displayedwaveform thereof; and

means for selectively providing a display of said first verticaldeflection signal or said second vertical deflection signal.

2. An oscillographic instrument for providing a display of electricalsignals, said instrument comprising:

first vertical amplifier means for generating a first verticaldeflection signal in accordance with the amplitude of a first electricalinput signal for determining the amplitude of the waveform thereof;horizontal deflection means generating a horizontal deflection signalfor providing a time-base sweep signal, said horizontal deflection meansincluding a trigger generator portion thereof for producing a triggersignal to initiate said time-base sweep signal, said trigger generatorcomparing the substantially varying voltage of said second electricalsignal to a selective reference voltage therein and said trigger signalbeing produced when the instantaneous voltage of said second electricalsignal is equal to said reference voltage;

second vertical amplifier means for receiving said second electricalsignal and said selective reference voltage from said trigger generatorand generating a second vertical deflection in response thereto; and

vertical deflection means including switching means for selectivelyproviding a display of either or both of said first vertical deflectionand said second vertical deflection signal.

3. The oscillographic instrument according to claim 2 wherein saidsecond vertical amplifier means comprises a balanced differentialamplifier receiving respectively at a pair of input terminals thereinsaid second electrical signal and said reference voltage therebyproducing said second vertical deflection signal differentially at apair of output terminals therein.

4. The oscillographic instrument according to claim 3 wherein saidsecond vertical amplifier means also includes delay means for providingsubstantially matched time delay between said first and second verticalamplifier means.

5. The method of displaying an auxiliary electrical signal by anoscillographic instrument including a first vertical deflection meansgenerating a first vertical deflection signal in accordance with theinstantaneous amplitude of a primary electrical input signal andincluding horizontal deflection means generating a horizontal deflectionsignal in response to the comparison of said auxiliary electrical signalto a selective reference voltage in a trigger generator portion thereof,said method comprising;

applying said auxiliary electrical signal to a first input terminal of asecond vertical deflection means while applying said reference voltageto a second input terminal of said second vertical deflection means,

generating a second vertical deflection signal in accordance with theinstantaneous amplitude of said auxiliary signal and the level of saidreference voltage,

delaying said second vertical deflection signal to provide a time matchwith said first vertical deflection signal, and

selectively displaying said first vertical deflection signal and/or saidsecond vertical deflection signal. 6. The method according to claim 5wherein said auxiliary signal is an external triggering signal.

7. An oscilloscope having means to provide a display of an externaltriggering signal while said signal is activating a sweep generatorportion thereof, said means comprising:

trigger-view amplifier means receiving an input from a trigger generatorportion of said oscilloscope, said input including said externaltriggering signal and a triggering level reference voltage, and

switching means selecting a display signal from normal verticalamplifier channel means and/or said trigger-view amplifier means.

8. The oscilloscope according to claim 7 wherein said trigger-viewamplifier means is a balanced differential amplifier including delayingmeans to provide a time match between signals processed by saidtrigger-view amplifier means and a normal vertical amplifier means ofsaid oscilloscope.

9. The oscilloscope according to claim 7 wherein said display of saidexternal triggering signal includes triggering level and triggeringslope information such that the sweep-initiating point is determinablefrom the waveform thereof.

1. In an oscillographic instrument for providing a display of electricalsignals; said instrument including vertical deflection means forgenerating a first vertical deflection signal in accordance with theinstantaneous amplitude of a first electrical input signal fordetermining the amplitude of a waveform thereof; said instrument alsoincluding horizontal deflection means for generating a horizontaldeflection signal for providing a timebase sweep signal, said sweepsignal being generated in response to the output of a trigger comparatormeans whose inputs are a selective second electrical input signal and aselective reference voltage, wherein said second electrical signal iscompared to said selective reference voltage; the improvementcomprising: means for receiving said second electrical and saidselective reference voltage from said trigger comparator means andgenerating a second vertical deflection signal in response thereto, saidsecond vertical deflection signal being generated in accordance with theamplitude of said second electrical signal and in comparison to saidreference voltage for determining the sweep-initiating point on thedisplayed waveform thereof; and means for selectively providing adisplay of said first vertical deflection signal or said second verticaldeflection signal.
 2. An oscillographic instrument for providing adisplay of electrical signals, said instrument comprising: firstvertical amplifier means for generating a first vertical deflectionsignal in accordance with the amplitude of a first electrical inputsignal for determining the amplitude of the waveform thereof; horizontaldeflection means generating a horizontal deflection signal for providinga time-base sweep signal, said horizontal deflection means including atrigger generator portion thereof for producing a trigger signal toinitiate said time-base sweep signal, said trigger generator comparingthe substantially varying voltage of said second electrical signal to aselective reference voltage therein and said trigger signal beingproduced when the instantaneous voltage of said second electrical signalis equal to said reference voltage; second vertical amplifier means forreceiving said second electrical signal and said selective referencevoltage from said trigger generator and generating a second verticaldeflection in response thereto; and vertical deflection means includingswitching means for selectively providing a display of either or both ofsaid first vertical deflection and said second vertical deflectionsignal.
 3. The oscillographic instrument according to claim 2 whereinsaid second vertical amplifier means comprises a balanced differentialamplifier receiving respectively at a pair of input terminals thereinsaid second electrical signal and said reference voltage therebyproducing said second vertical deflection signal differentially at apair of output terminals therein.
 4. The oscillographic instrumentaccording to claim 3 wherein said second vertical amplifier means alsoincludes delay means for providing substantially matched time delaybetween said first and second vertical amplifier means.
 5. The method ofdisplaying an auxiliary electrical signal by an oscillographicinstrument including a first vertical deflection means generating afirst vertical deflection signal in accordance with the instantaneousamplitude of a primary electrical input signal and including horizontaldeflection means generating a horizontal deflection signal in responseto the comparison of said auxiliary electrical signal to a selectivereference voltage in a trigger generator portion thereof, said methodcomprising: applying said auxiliary electrical signal to a first inputterminal of a second vertical deflection means while applying saidreference voltage to a second input terminal of said second verTicaldeflection means, generating a second vertical deflection signal inaccordance with the instantaneous amplitude of said auxiliary signal andthe level of said reference voltage, delaying said second verticaldeflection signal to provide a time match with said first verticaldeflection signal, and selectively displaying said first verticaldeflection signal and/or said second vertical deflection signal.
 6. Themethod according to claim 5 wherein said auxiliary signal is an externaltriggering signal.
 7. An oscilloscope having means to provide a displayof an external triggering signal while said signal is activating a sweepgenerator portion thereof, said means comprising: trigger-view amplifiermeans receiving an input from a trigger generator portion of saidoscilloscope, said input including said external triggering signal and atriggering level reference voltage, and switching means selecting adisplay signal from normal vertical amplifier channel means and/or saidtrigger-view amplifier means.
 8. The oscilloscope according to claim 7wherein said trigger-view amplifier means is a balanced differentialamplifier including delaying means to provide a time match betweensignals processed by said trigger-view amplifier means and a normalvertical amplifier means of said oscilloscope.
 9. The oscilloscopeaccording to claim 7 wherein said display of said external triggeringsignal includes triggering level and triggering slope information suchthat the sweep-initiating point is determinable from the waveformthereof.